Synthetic polymeric thermoplastic compounds have found widespread application as packaging materials, packing materials, and as molded articles and the like, replacing many traditional materials such as paper, wood, steel, and aluminum. A problem that is growing increasingly acute is how to treat these thermoplastics after their useful life is finished. In many situations, the immediate solution is to landfill the thermoplastics or to recycle. However, disposing of thermoplastics along with other trash and garbage as refuse is seen as wasteful, while on the other hand, for many applications recycling is not an economic or practical option. The alternatives are to combine the used thermoplastics with other organic materials in a composting facility, subject the plastic material to soil burial, or to submerge the thermoplastics in underwater disposal.
As a solution, the present invention describes a process for formulating the thermoplastics with a directly biodegradable component and other additives to provide a degradable synthetic polymeric compound. This compound is vulnerable to chemical, photochemical, and biodegradation mechanisms brought about by inclusion of the compound into a suitable degradation environment, such as in a composting facility, in soil burial, or submersion of the thermoplastics. Then, after a period of time, which is considerably less than if the synthetic polymeric compound were not so formulated, the only products that will remain will be innocuous products devoid of their original structure, or the compound will be assimilated into biomass.
It is therefore an object of the present invention to provide an improved degradable synthetic polymeric thermoplastic compound. This synthetic compound needs to be suitable for use as a packaging material, packing material, or as a blow molded or injection-molded object and the like, and then, upon completion of its useful life, suitable for soil burial or water disposal or inclusion in a composting facility where the compound will undergo degradative breakdown to reduce the thermoplastic component to innocuous by-products. This requires that the synthetic polymeric compound maintain its structural integrity while it is being used for its intended purpose and then, upon completion of that purpose, break down under the action of degradation mechanisms occurring in suitable environments, and in a relatively short period of time. Towards this end, incorporation of an anti-oxidant or stabilizing component, which is active over a limited period of time to retard commencement of the start of the degradation process, may be preferred. Then, on depletion of part of the anti-oxidant or stabilizing component and in the presence of an oxidizable component, degradative change of the thermoplastic polymers into lower molecular weight fragments begins.
Along its path from useful article to innocuous products, the synthetic polymeric compound undergoes three degradation stages. These stages are not necessarily sequential, but can occur simultaneously in cooperative action to bring about the resultant degradation. The first stage is biological removal of the directly biodegradable component or components which results in a mass reduction of the synthetic polymeric compound to give a highly porous material. In some cases, this leads to fragmentation of the synthetic compound to form polymeric dust. The enhanced porosity increases the exposed surface area of the long chain hydrocarbons and/or synthetic polymers and renders them more vulnerable to chemical attack. The second stage is chemical and results in an oxidative shortening of the long chain polymers to decrease their molecular weight. At some point, the third stage begins with the biological metabolism of the low molecular weight fragments. The synthetic polymeric compounds of the present invention thus preferably include a directly biodegradable component, stabilizing component having a limited effective period and an oxidizable component. The latter generates a peroxide or a hydroperoxide that serves to oxidize the many carbon-to-carbon linkages of the polymer under the influence of a natural decomposition environment after the limited effective period of the stabilizing component has ceased.
Preferred oxidizable materials are unsaturated polymer-soluble compounds such as derivatives of unsaturated fatty acids that contain at least one double bond per molecule, e.g. esters or natural fats themselves or other unsaturated materials, such as unsaturated rubber. The oxidation of compounds such as fats can be catalyzed by transition metals such as iron. An aromatic ketone is a preferred additive because it has a synergistic effect on the oxidation reactions. The aromatic ketone is also useful as a photodegradation enhancer.